Heat treatment of chromium alloy steels



June 30, 1936. F. M. BECKET ET AL HEAT TREATMENT OF CHROMIUM ALLOY STEELS Original Filed April 9, 1934 La -*2 Fi -"3 MQDB qk MAE wk DILAT/ON D/LAT/ON D/LAT/ON DILATION 3E ENSE D/LAT/ON INVENTORS FREDERICK M. BECKET BY RUSSELL FRANKs ATTORN EY Patented June 30, 1936 HEAT TREATMENT OF CHROM'IUM ALLOY STEELS Frederick M. Becket, New York, and Russell Franks, Niagara Falls, N. Y.. assignors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Original application April 9, 1934, Serial No. 719,756. Divided and this application May 8,

1935. Serial No. 20,332

4 Claims. (01. 148-215) chromium with and without titanium are given The invention relates to a process of heat treating certain chromium-containing steels, by heating and cooling them, either slowly or rapidly, from temperatures above or below those at which the thermal changes ordinarily occur in the ferritic types of chromium-bearing steels. This application'is a division of our application Serial No. 719,756 filed April 9, 1934.

When chromium is added to a steel the critical m temperature range of the steel is raised appreciably, and the product can be fully softened only by heating for comparatively long periods at temperatures slightly below the critical range, fol-.

. lowed by slow cooling. For example, a hotworked steel, containing about 0.12% carbon and 12% chromium cannot be fully softened unless it is held for a period of several hours at temperatures notgreater than about 800? C. After holding such steel at this temperature for a suflicient period of time it is necessary tocool it slowly in order to attain the softness desired. Such a procedure is carried out to prevent the metal from air hardening. The

extent to-which a given steel air hardens depends on its chromium and carbon contents.

1! substantially all 01 the carbon present in the chromium-bearing metal is in combination with elements such as titanium and columbium, instead of chromium or iron, or both, the steel can be rendered soft and ductile by holding it for a period of onlya few minutes, instead of hours, at

temperatures within a range from somewhat be- 10W to somewhat above the normal critical range of chromium steels. Also, these steels can be cooled from'these temperatures either rapidly or slowly without greatly impairing their properties. The economic advantage of such a process for annealing chromium steels is apparent.

An object of the invention is to provide a method 01 heat treating chromium steels wherein substantially all of the carbonpresent is in combination with titanium or columbium.

The results of a few tests conducted on sheet steels of twenty gage containing up to about 14% in Table No. I. 1

Table No. I

Erichf? c1- o Ti Condition 0! steel sen 17%..

value values 5. 76 0.12 As rolled 4. 80 I 113 5. 76 0. l2 Heated at 050 C. 4 hrs. and 6. 98

1 air cooled. 5. 76 0. l2 Heated at 750 0.10min. and 7. 100

a cooled. 5. 76 0. l2 Heated at 750 C. 4 hrs. and 8. 00 85 a cooled. 5. 76 0.12 Heated at 900 C. 10 min. and 4. 90 110 air cooled.

5. 93 0. l3 0. 90 As rolled 8. 20 86 5.93 0. 13 0.90 Heated at 650 C. 4 hrs. and 8. 10 79 air cooled. 5. 93 0. l3 0. 90 Heated at 750 C.10mln. and 8. 80 76 air cooled.

5.93 0. 13 0.90 Heated at 750 C. 4 hrs. and 9.90 63 air cooled. 6. 93 0.13 0. 90 Heated at 900 0. 10min. and 9. 20

air cooled.

13. 60 0. 13 As roller] 5. 00 113 13. 60 0. l3 Heated at 650 C. 4 hrs. and 6. 50 98 air cooled. 13. 60 0. l3 Heated at 650 0. 12 hrs. and 7. 00 89 furnace cooled. 13. 60 0. 13 Heated at 750 C. 10 min. and 7. 50 96 air cooled. 13. 60 0.13 Hearted at 750 C. 4 hrs. and 8.40 76 a 00 e 13. 00 0. l3 Hosted at 900 C. 10min. and 4. 112

air cooled. 13.60 0. l3 Heated at l000 C. 5min. and 5.00 100 air cooled.

13.35 0. 11 0. A5 rolled 8. 10 88 13. 35 0. ll 0. 85 Heated at 650 C. 4 hrs. and 8.3) 82 air cooled.

13. 35 0.11 0. 85 Heated at 650 C. 12 hrs. and 8. 65 81 furnace cooled. 13. 35 0. l1 0. 85 Heilirted at 750 0. 10min. and 8. 00 80 a coo 13. 35 0. ll 0. 85 Heated at 750 C. 4 hrs. and 9. (I) 70 r coo 13. 35 0. ll 0. 85 Heated at 9(1) 0. 10min. and 9. 30 70 air cooled. 13.36 0. ll 0. 85 Heatedatl000 0.5mln. and 68 air cooled.

Table I shows clearly that the titanium-conrolled state and cannot be rendered sufficiently ductile and soft unless they are heldfor comparatively longer periods at the proper temperatures. As indicated in Table II, the addition of the proper amount of titanium to these steels renders them capable of being made soft and ductile by heating for only a few minutes at temperatures up to about 1000 C.

Table No. II

Erich- 9', Cr O Ti Condition oi steel sen u value value 18.29 0.06 3 Aarolled 5.25 as 18.29 0.06 Heated at 750 C. 4 hr. and 7.00 76 air coole 18.29 0.06 Heatedat9000.l0min. and 50 83 air cooled. 18.29 0.06 Heated at 1000 C. 5 min. 2.70 83 and air cooled.

18.00 0. 13 0. 78 As rolled 7.00 72 18.00 0.13 0.78 Hg a ted at 750 C. 4 hr. and 7.00 74 coo 18.00 0.13 0.78 Heatedat 900 0.10min. and 9.00 66 air cooled. 18.00 0.13 0 78 Heated at 1000 C. 5 min. 9.00 69 and air cooled.

Similar results are obtainable by the use of columbium instead of the titanium.

The effects of titanium and columbium on chromium steels is further elucidated by dilatometric tests. Dilation curves obtained in tests on chromium steels with and without additions of titanium and columbium are shown in the accompanying drawing, in which Figure 1 is a dilation curve obtained on a steel containing 5.56% chromium, 0.10% carbon, remainder substantially all iron.

Figure 2 is 'a dilation curve of a steel containing 5.93% chromium, 0.13% carbon, 0.90% titanium, remainder substantially all iron.

Figure 3 is a dilation curve of a steel containing 5.75% chromium, 0.05% carbon, 0.75% titanium, remainder substantially all iron,

Figure 4 is a dilation curve of a steel containing 5.85% chromium, 0.10% carbon, and 1.08% columbium, remainder substantially all iron,

Figure 5 is a dilation curve of a steel containing 13.17% chromium, 0.12% carbon, remainder substantially all iron,

Figure 6 is a dilation curve of a steel containing 13.55% chromium, 0.11% carbon, 0.85 %titanium, remainder substantially all iron.

Referring to Figures 1, 2, 3, and 4, it is seen that an effect of the titanium or the columbium on steels of the 5% chromium type is to raise considerably the AC-l point, and'to raise the AR-l point even more, the latter being brought nearly to the temperature of the AC-l point.

It is unnecessary in the present invention to maintain a maximum of 0.10% carbon in order to insure maximum softness and workability, because if suitable amounts of titanium are present equally soft steels may be obtained with somewhat higher carbon. strated by Table III, in which are given the hardness and Erichsen values of 13% chromium steels, low and high in carbon, in the as-rolied state and when heat treated by heating at 1000 C. for five minutes and then air cooled.

The method of the invention can be applied to metal containing between 4% and 30% chromium, a suitable proportion of titanium or columbium, not over 0.50% (preferably not over 0.25%) carbon, and the remainder chiefly iron. Such metals will also contain the usual amounts of manganese and silicon that are employed for deoxidizing purposes. To attain substantially its full effect in facilitating the softening heat-treatment, the percentage of titanium present in the steel should be at least three times (and preferably four to six times) the percentage of carbon. When columbium is used, its percentage should This is clearly demonbe at least six times (and preferably eight to ten times) the carbon percentage. Larger proportions of the softening metal may be used but we prefer that the percentage of titanium or columbium in the steeLshall not exceed its respective stated preferred minimum value by more than we claim:

1. Method oi heating treating ferritic steels containing about 4% to 30% chromium: carbon in an amount "not over about 0.50%; columbium, the columbium content being at least about eight times the carbon content and being not more than eight times the carbon content plus about 1.5% the remainder principally iro heating the steel to a temperature between about perature for a time not over about two hours. and then cooling it to room temperature which comprises 700" c. and about 1000 0., holding it at said tem- 2. Method of heat treating ferritic steels containing about 4% to 30% chromium; carbon. in an amount not over about 0.25%; columbium, the columbium content being at least about eight times the carbon content and being not more than eight times the'carbon content plus about 1.5%; the remainder principally iron; which comprises heating the steel to a temperature between about 800 C. and about 900 (2., it at said temperature for a time not overt-bout an hour,

and then rapidly o ling it to room temperature. 3..Method of heat treating ferritic st'eels'containingabout4%to80%chromium;carbonin anamount notover about 0.25%; columbium. e. 7

columbium content being at least about eight times the carbon content and being not more than eight times the carbon content plus about 1.5%; the remainder principally iron; which comprises heating the steel to a temperature between about 800 C. and about 900 C., holding it at said temperature for a time not over about an hour, and then air cooling it to room temperature.

4. As an article of manufacture, the product 0! the process defined in claim 1.

FREDERICK M. BECKET. RUSSELL FRANKS. 

